This invention relates to a catalyst component and system suitable for use in the polymerization of alpha olefins and to a process employing the catalyst system.
Catalyst systems composed of a titanium halide and an organoaluminum compound have been widely used in the polymerization of alpha olefins. However, the basic two-component catalyst system has disadvantages that prior art researchers have recognized and attempted to obviate. Thus, with some alpha olefins these systems generally result in the formation of a polymer having a substantial amount of amorphous, or hydrocarbon soluble polymer, which must be separated from the desired crystalline, or hydrocarbon insoluble product. The production of stereoregular, crystalline polymers is a particularly desirable objective in many olefin polymerization processes.
In addition to the goal of providing stereoregular polymers, catalyst activity is an important factor in this area. Thus, it is economically important that higher amounts of polymer be formed per unit time per unit of catalyst employed in the polymerization process.
Various approaches to solving the aforementioned problems have been proposed in the art. Thus, it is known that the reduction of titanium terahalide with aluminum or hydrogen followed by grinding provides a catalyst of increased activity when the ground component is admixed with an organoaluminum compound. However, the increased activity is offset by the production of large amounts of amorphous polymer. U.S. Pat. No. 3,701,763 to S. Wada et al teaches that stereoregular polymers can be provided if the titanium trichloride component is pulverized in the presence of a large amount of auxiliary components, including certain aliphatic and aromatic ethers, amines and ketones, until the .alpha. or .gamma.- type of the X-ray diffraction pattern of the crystal form of the titanium trichloride cannot be identified, and the resulting titanium trichloride composition extracted with certain solvents. In U.S. Pat. No. 3,850,899, also to S. Wada et al., the solvent used to extract the titanium trichloride composition can be one of these ketones. The use of aliphatic and aromatic ketones is also described in U.S. Pat. No. 3,210,332 to H. D. Lyons and C. W. Moberly, which teaches the in situ addition of these ketones to a polymerization process employing the conventional alkyl aluminum-titanium trichloride catalyst in order to maximize the production of stereoregular polymer.
While conferring some improvement on the properties of the resultant polymer, many of the prior art auxiliary components present disadvantages that are not off-set by an improvement in polymer properties. For example, hexamethyl phosphoramide, a widely used auxiliary component, recently has been found to be carcinogenic, and dimethylpropionamide is reported to be a possible carcinogen. Many of the ethers used as auxiliary components are highly flammable, autooxidizable liquids capable of producing explosive peroxides.
Aromatic ketones such as benzophenone and substituted benzophenones are known photosensitizers, a characteristic which could affect the stability of the resultant polymer. Other aromatic ketones such as benzanthrone and benzosuberone have been found to provide polymers having a low isotactic content.
Now it has been found in accordance with this invention that catalyst systems containing selected terpenic ketones are efficacious for the preparation of polyolefins, and obviate many of the drawbacks inherent in prior art auxiliary components.